Multilayer mattress

ABSTRACT

A multilayer mattress comprising a top polyurethane polyether reticulated foam layer; a middle polyurethane polyether reticulated foam layer; and a bottom support layer. The top layer has an open-cell structure, a thickness of 1.5-5 cm, a compression resistance of 1-5.5 kPa and a resilience of 40-55%; whereas the middle layer has an open-cell structure, a thickness of 2.5-7.5 cm, a compression resistance of 1-5.5 kPa and a resilience of 1-15%.

FIELD OF THE INVENTION

The present invention generally relates to the field of mattresses. More specifically, the present invention relates to a mattress made up of multiple layers of different materials.

BACKGROUND OF THE INVENTION

The use of viscoelastic materials in the manufacture of mattresses is currently widespread. Viscoelastic materials can have different densities, which allow obtaining different sensorial effects of the final mattress.

Viscoelastic foam (also known as memory foam) is a polyurethane foam. Polyurethane polymers are formed by reacting an isocyanate with a polyol. Polymeric polyols are usually polyethers or polyesters.

Viscoelastic mattresses adapt to the shape of the body when sleeping, therefore increasing comfort; however, they usually have heat-related issues mainly due to the fact that they do not allow enough air flow to dissipate body heat. Viscoelastic mattresses absorb body heat and remain warm for a long time, therefore preventing the body from cooling down while sleeping and forcing other heat elimination mechanisms to take place (such as sweating, for example). Despite their ability to adapt to the shape of the body, these heat-related issues lower their overall performance and can reduce the quality of sleep that can be achieved.

One solution known in the prior art to overcome this problem is the use of a gel-like material. In this case, a gel material is inserted in the top layer of the mattress. The gel provides an immediate coolness feel. However, when sufficient amounts of gel are used (such as a layer of gel) the final mattress is not breathable and therefore comfort is reduced. When smaller amounts of gel are used the initial coolness feel is not efficient. Furthermore, gel materials have a high heat conductivity which means they absorb body heat very fast, but they also reach a heat balance very soon and therefore prevent heat or moisture dissipation. Briefly, the use of gel-like materials in the top layer of a mattress provides an initial feeling of “coolness”, but soon after this material reaches a balance with the body temperature and fails to provide heat elimination throughout the night. Therefore, the quality of long-term sleep (throughout the night) with these mattresses is not sufficient.

Other solution known in the prior art is the use of ventilation channels, such as series of cylindrical or prismatic cuts on the surface of the mattress in oblique direction, which allow the air being in contact with the body to escape through the sides of the mattress.

The use of polyurethane reticulated foam for air-filtering purposes is also known. For these applications, polyurethane foams are polyester-based foams. Such foams are designed to filter air and not for commodity purposes, they are very hard and not suitable for use in mattress manufacturing.

Therefore, there is still a need in the art for a comfortable mattress having good heat dissipation capacity, allowing the body temperature to cool down and stay cool in the long term, therefore providing good sleep quality throughout the night. It is also desirable for the mattress to have a good moisture dissipation capacity, allowing any sweat to be dissipated, therefore improving sleep quality even in very warm environments.

SUMMARY OF THE INVENTION

In order to overcome the above-mentioned drawbacks of the prior art, the present invention, in at least some embodiments, discloses a multilayer mattress comprising a top polyurethane polyether reticulated foam layer; a middle polyurethane polyether reticulated foam layer; and a bottom support layer.

The top layer has an open-cell structure, a thickness of 1.5-5 cm, a compression resistance of 1-5.5 kPa and a resilience of 40-55%; whereas the middle layer has an open-cell structure, a thickness of 2.5-7.5 cm, a compression resistance of 1-5.5 kPa and a resilience of 1-15%.

The purpose of the bottom support layer is mainly to adjust the thickness of the final mattress, and as such it is not specifically restricted. Any standard support material known in the mattress manufacturing industry (such as regular foam, latex, springs, etc.) can be used in conjunction with the present invention as the bottom support layer.

Without wishing to be limited to a closed list, due to the use of the top and middle layer, which have an open-cell structure, the multilayer mattress according to at least some embodiments of the present invention provides at least the following advantages over the prior art:

-   -   It expels moisture and heat which is produced by the body while         sleeping;     -   The mattress remains dry and therefore the user stays dry during         the night;     -   Maximum moisture drainage and constant air circulation is         provided from the use of reticulated, open-cell foam;     -   Multilayer construction using reticulated, open-cell foam having         different resilience and memory characteristics allows for         perfect body alignment with maximum comfort and pleasant sense         of pressure relief.

BRIEF DESCRIPTION OF THE DRAWINGS

Further features and advantages of the present invention will become apparent from the detailed description of a preferred embodiment which follows, when considered together with the attached drawings. The attached drawings are provided for illustrative purposes only, and should not be construed as limiting the scope of the invention in any way.

In the drawings:

FIG. 1 shows a cross-sectional view of a multilayer mattress according to the preferred embodiment of the present invention.

FIG. 2 is a graph showing thermography data corresponding to a multilayer mattress according to the preferred embodiment of the present invention, as well as two mattresses according to the prior art for comparison purposes.

DETAILED DESCRIPTION OF THE INVENTION

As shown in FIG. 1, the mattress according to an embodiment of the present invention is made up of three different layers.

The top layer (1) is a reticulated foam layer made of polyether-based polyurethane and having an open-cell structure. The thickness of the top layer is preferably 1.5-5 cm, most preferably 2 cm. The compression resistance of the top layer is preferably 1-5.5 kPa, more preferably 1.3-5.5 kPa, still more preferably 3.5-5.5 kPa, most preferably 3.5 kPa. The resilience of the top layer is preferably 40-55%, most preferably 50%.

In another embodiment of the invention, compression resistance of the top layer is preferably 1.3 kPa. In this case softer version of the mattress is obtained in comparison with the version having compression resistance of at least 3.5 kPa. Accordingly, a different degree of hardness of the mattress can be obtained, maintaining suitable heat and moisture dissipation capabilities.

The top layer may optionally be in direct contact with the body (or at least may optionally be the uppermost layer of the mattress to contact the body, optionally with a sheet or other bedclothes between this layer and the body). The open-cell structure of this top layer forms an air chamber allowing sufficient airflow therethrough and therefore allowing heat dissipation.

The middle layer (2) is also a reticulated foam layer made of polyether-based polyurethane and having an open-cell structure. The thickness of the middle layer is preferably 2.5-7.5 cm, more preferably 4-6 cm, most preferably 4 cm. The compression resistance of the middle layer is preferably 1-5.5 kPa, more preferably 1-3 kPa, most preferably 1.24 kPa. The resilience of the middle layer is preferably 1-15%, most preferably 7%.

The cells in the structure of the middle layer are opened to a lesser extent compared to the cells in the structure of the top layer. The middle layer therefore allows adaptability of the mattress to the shape of the body when sleeping, while still adding to the heat dissipation effect achieved by the top layer.

Therefore, such construction of the top and middle layers allows overall adaptability of the mattress to the shape of the body (as in the case of standard viscoelastic mattresses), while providing a breathability (and therefore both heat and moisture dissipation) that cannot be achieved with standard viscoelastic mattresses.

The flexible foams obtained from slab stock production partially contain closed cells. The foams adapt to the shape of the body when sleeping, therefore increasing comfort, but have poor heat and moisture dissipation capabilities. In reticulated foams, all the residual cell membranes are melted and a completely open cellular network is obtained by a thermal process (explosion of oxygen-hydrogen in a closed reactor). The formulation of the cells in the top and middle layer of the multilayer mattress according to at least some embodiments of the present invention can be controlled during the manufacturing process (reticulation of the foam-process known to the one skilled in the art), as opposed to the random cellular structure of regular foam. During the reticulation process, open pentagonal dodecahedral cells are formed, which allow for constantly airflow inside the mattress. As mentioned above, this particular open-cell structure allows air circulation, which acts as a natural refrigeration element by means of heat dissipation. At the same time, this type of open-cell foam does not retain moisture (i.e., sweat. Reticulation techniques are commonly used manufacturing processes known by those skilled in the art, although they have not been previously applied to the mattress structures described herein.

As mentioned above, the polyurethane foam used in the manufacture of the top and middle layers is based on polyethers. Therefore, not only does it allow the aforementioned airflow, but it is also softer, more flexible and more resistant to hydrolysis compared to standard polyester-based foams.

The bottom layer (3) of the mattress according to at least some embodiments of the present invention may optionally be implemented in various ways. For example, any of the commonly used supports (such as regular foam, latex, springs, etc.) can be used as the bottom layer in the multilayer mattress of the present invention.

The mattress according to the present invention can be easily adapted to special needs of the user by simply varying the thickness of the top and middle layers (preferably within the aforementioned ranges), and especially by varying the thickness of the bottom support layer.

Unless otherwise specified herein, the compression resistance of the mattress is measured according to ISO 3386/1 and the resilience of the mattress is measured according to ISO 8307.

Examples

The following tests were performed in order to determine the water vapor permeability index using specimens of a mattress according to the present invention as well as specimens of mattresses according to the prior art for comparison purposes. Thermography tests were also performed using the mattress according to at least some embodiments of the present invention and according to the prior art.

1.1. Water Vapor Resistance:

Water vapor resistance of different specimens was tested according to UNE-EN 31092:1996.

The test surface was inside a climatic chamber at 35° C. and 40% RH.

The measurement surface was a 20×20 cm porous plate. The porous plate was heated at 35° C., and a controlled flow of water was supplied to its bottom surface through two communicating tubes. One of the tubes reached the bottom surface of the porous plate and the other one reached an electrode, thus always maintaining the same level of water in the porous plate.

The water supplied to the bottom surface of the porous plate went through the plate and reached the top surface. Therefore, the top surface of the plate was wet and at 35° C. In order to mimic the sweating behavior of the skin, a porous film was placed on the porous plate. The film has a pore size slightly larger than water vapor but smaller than water in liquid state. The water in liquid state reaching the top surface of the porous plate can only go through the film and into the space of the climatic chamber by changing to vapor state. This transformation was achieved by continuously drying the atmosphere in the chamber. Since the top surface of the plate has 100% humidity and the atmosphere in the chamber has 40% humidity, the diffusion process was spontaneous.

Since water in liquid state was changed to water vapor, energy consumption was observed, and the heat applied was the heat of vaporization of water at 35° C. (temperature in the climatic chamber). Said energy consumption depended on the specimen being tested, which was placed on top of the porous film.

The relative humidity can be expressed as pressure units at a given temperature as follows:

100% RH=5620 Pa

40% RH=2250 Pa

Therefore, the pressure difference in the climatic chamber was 3370 Pa.

That is, the test was based on the energy that needs to be supplied to a given area in order to maintain a pressure gradient.

The formula used to calculate the water vapor resistance was as follows:

Ret=(ΔP×area)/flow

where

Ret is the water vapor resistance (m² Pa/W);

ΔP is the pressure difference between the top surface of the plate and the atmosphere (3370 Pa);

the area of the plate is 0.04 m² (20×20 cm); and

the flow is the energy (in watts) supplied to the plate in order to maintain said pressure difference.

If the specimen placed on top of the porous film allowed water diffusion therethrough, the water would change into vapor and energy consumption would be observed. Therefore, the more breathable the specimen is (the water vapor resistance is smaller), the greater the energy consumption that is measured.

Conversely, if the specimen was waterproof, the water cannot get to the climatic chamber atmosphere and there would be minimal energy consumption (low breathability).

The following Table 1 shows the test results for a mattress according to the present invention (specimen A) and a mattress according to the prior art (specimen B). Three specimens of each mattress (A1, A2 and A3; B1, B2 and B3) were tested and the average was calculated.

The prior art mattress was S climatic mattress and has a 2.5 cm thick top polyurethane layer with gel insertions, as well as several other polyurethane foam layers acting as a support.

TABLE 1 Water vapor resistance Specimen (m²Pa/W) A A1 96.78 A2 96.61 A3 96.93 Average 96.77 B B1 117.44 B2 116.88 B3 117.12 Average 117.15

Table 1 shows that the mattress according to the present invention has a lower water vapor resistance compared to the prior art, and therefore it is more breathable.

1.2. Thermal Resistance:

The thermal resistance was tested again according to UNE-EN 31092:1996, and it is the temperature difference between two sides of a material divided by the resulting heat flow per surface unit in the direction of the gradient.

Once again, the test surface was a 20×20 cm plate, and it was heated at 35° C.

The plate was placed inside a controlled climatic chamber at 20° C. Air was supplied 14 cm above the plate at a flow rate of 1 m/s.

In order to maintain the plate temperature at 35° C. inside a climatic chamber at 20° C., energy flow must be supplied to said plate. Otherwise, the plate would cool down.

A specimen was placed on top of the plate. Therefore, the less energy that was supplied to the plate in order to keep it at 35° C., the more insulating the specimen was.

The formula used to calculate the thermal resistance was as follows:

Rct=(ΔT×area)/flow

where

Rct is the thermal resistance (m²K/W);

ΔT is the temperature difference between the plate and the atmosphere (35° C.-20° C.);

the area of the plate is 0.04 m² (20×20 cm); and

the flow is the energy (in watts) supplied to the plate in order to maintain said temperature difference.

Therefore, the greater the thermal resistance, the more insulating the material is.

The following Table 2 shows the test results for a mattress according to the present invention (specimen A) and a mattress according to the prior art (specimen B). Three specimens of each mattress (A1, A2 and A3; B1, B2 and B3) were tested and the average was calculated.

The prior art mattress was the same as in the previous test for water vapor resistance.

TABLE 2 Thermal resistance Specimen (m²K/W) A A1 1.2516 A2 1.3915 A3 1.3105 Average 1.3179 B B1 1.1427 B2 1.1889 B3 1.1583 Average 1.1633

Table 2 shows that the mattress according to the present invention has a greater thermal resistance compared to the prior art, and therefore it is more insulating.

1.3. Water Vapor Permeability Index:

The water vapor permeability index represents the relationship between water vapor resistance and thermal resistance, previously calculated, according to the following formula:

i _(mt) =S×Rct/Ret

where

i_(mt) is the water vapor permeability index;

Rct is the thermal resistance;

Ret is the water vapor resistance; and

S is equal to 60 Pa/K.

The water vapor permeability index has no unit and may have values between 0 and 1.

A value of 0 means that the material is waterproof and therefore has an infinite water vapor resistance, causing discomfort to the user.

A value close to 1 means that the material has both the thermal resistance and the water vapor resistance of a layer of air having the same thickness.

Therefore, the closer the water vapor permeability index is to 1, the better the mattress is.

The following Table 3 summarizes the water vapor permeability index values for the mattresses used in the previous examples to test the water vapor resistance and the thermal resistance.

TABLE 3 Water vapor Thermal Water vapor resistance resistance permeability (m²Pa/W) (m²K/W) index A 96.77 1.3179 0.82 B 117.15 1.1633 0.60

The mattress according to the present invention has a higher water vapor permeability index compared to the prior art, and therefore it will provide greater comfort to the user.

2. Thermography

Thermography tests were performed using a thermography camera on a mattress according to the present invention as well as mattresses according to the prior art for comparison purposes.

Thermography tests quantify the temperature variation of the mattress after being exposed to a temperature similar to body temperature.

A sample mattress was placed inside a climatic chamber at 20° C. and 60% RH. A mannequin was internally heated at a constant temperature of 35° C. and placed lying on the sample mattress for 1 hour. Then the mannequin was placed in a sitting position, and the thermography camera recorded the surface temperature of the area of the mattress where the mannequin had been lying. Measures were taken at 10-second intervals for 17 minutes. FIG. 2 shows a graph representing the thermography results for a mattress according to the present invention (A), an S Climatic mattress as described hereinabove (B) and a standard viscoelastic mattress of the prior art (C).

The following Table 4 shows the maximum and minimum temperature reached by each of said mattresses in this test.

TABLE 4 A B C Maximum 29.0 33.9 31.1 temperature (° C.) Minimum 22.4 20.7 22.2 temperature (° C.)

As can be seen in Table 4, the initial temperature of the mattress according to the present invention is lower than the initial temperatures of the mattresses according to the prior art, which means that the mattress according to the present invention takes a longer time to reach body temperature and therefore maintains heat dissipation for a longer period of time.

As can be seen from FIG. 2, the mattress according to the present invention also dissipates its initial temperature more slowly than the two mattresses according to the prior art.

Although the invention has been described hereinbefore according to a specific embodiment, the invention should not be construed as being limited to said embodiment. Those skilled in the art can perform different variations and modifications to said embodiment without departing from the scope and spirit of the present invention, defined by the following claims. 

What is claimed is:
 1. A multilayer mattress comprising: a top polyurethane polyether reticulated foam layer, having an open-cell structure, a thickness of 1.5-5 cm, a compression resistance of 1-5.5 kPa and a resilience of 40-55%; a middle polyurethane polyether reticulated foam layer having an open-cell structure, a thickness of 2.5-7.5 cm, a compression resistance of 1-5.5 kPa and a resilience of 1-15%; and a bottom support layer.
 2. The multilayer mattress according to claim 1, wherein the top foam layer has a thickness of 2 cm.
 3. The multilayer mattress according to claim 1, wherein the top foam layer has a compression resistance of 1.3-5.5 kPa.
 4. The multilayer mattress according to claim 3, wherein the top foam layer has a compression resistance of 3.5-5.5 kPa.
 5. The multilayer mattress according to claim 4, wherein the top foam layer has a compression resistance of 3.5 kPa.
 6. The multilayer mattress according to claim 1, wherein the top foam layer has a resilience of 50%.
 7. The multilayer mattress according to claim 1, wherein the middle foam layer has a thickness of 4-6 cm.
 8. The multilayer mattress according to claim 7, wherein the middle foam layer has a thickness of 4 cm.
 9. The multilayer mattress according to claim 1, wherein the middle foam layer has a compression resistance of 1-3 kPa.
 10. The multilayer mattress according to claim 9, wherein the middle foam layer has a compression resistance of 1.24 kPa.
 11. The multilayer mattress according to claim 1, wherein the middle foam layer has a resilience of 7%.
 12. The multilayer mattress according to claim 1, wherein the cells in the structure of the middle layer are opened to a lesser extent compared to the cells in the structure of the top layer.
 13. The multilayer mattress according to claim 1, wherein it has a water vapor resistance of 96-97 m² Pa/W.
 14. The multilayer mattress according to claim 1, wherein it has a thermal resistance of 1.2-1.4 m²K/W.
 15. The multilayer mattress according to claim 1, wherein it has a water vapor permeability index greater than 0.8. 